In the treatment of abnormal curvatures of the spine, such as kyphosis, lordosis, and scoliosis, it is common to perform a surgical procedure on the patient whereby the curvature of the spine is altered so as to render it as normal as possible. For example, in the correction of scoliosis, anterior spinal instrumentation and fusion of two or more vertebrae has been a standard approach for at least the last 35 years. In such procedures, a thoracotomy incision is made, and a portion of the spine is exposed, particularly around the apex of the curve. The surgeon then may excise some or all of one or more intervertebral discs in the exposed spinal region. After removing the disc tissue, if that procedure is performed, the improperly curved vertebrae can then be implanted with corrective instrumentation and repositioned.
The surgeon selects appropriate bone anchors, commonly screws for fixation within a pedicle or other spinal portion, and fixes the bone anchors within two or more vertebrae to be repositioned. A rod or pin, which may be pre-contoured and/or contourable in situ, is fitted with the fixed bone anchors and held thereto. This is commonly accomplished by fitting a cap, set screw, or similar piece to the bone anchor, so that the rod is contained with the bone anchor, yet retains some freedom to move in response to the repositioning of the vertebrae.
After this instrumentation is implanted, the surgeon repositions the vertebrae. Repositioning occurs by compression of the bone anchors--i.e., the bone anchors are pushed toward each other--thereby moving the vertebrae to which they are fixed. To compress the bone anchors, it is known to use, among other relatively large tools, a scissor- or tongs-like device. Generally, the compressing device has two lever arms connected in an X-shape that can pivot with respect to one another. One end of each lever arm is gripped by the surgeon, and these hand-gripping ends are spread apart. The compressing ends, which are the ends opposite the hand-gripping ends, are placed in contact with the bone anchors. The surgeon then moves the gripping ends together, thereby forcing the compression ends and their corresponding bone anchors toward each other. In this way, the relative positions of two vertebrae are altered. Compression continues until the vertebrae correspond to the curvature of the spinal rod and/or to a normal or approximately normal spinal curvature. When the compression is finished, the set screws or caps fitted to the bone anchors can be tightened, fixing the bone anchors to the rod, and fixing the spine in its new curvature. Fusion of vertebrae or other treatment of the intervertebral spaces from which disc tissue was excised can then be performed.
Performing these tasks using traditional techniques and devices of open surgery has severable undesirable features and consequences. Initially, such open surgery requires a long thoracotomy, which incision leaves a relatively long and unappealing scar. Further, such surgery entails incision, retraction, and adjustment of numerous tissues in addition to the spinal tissues. As a result, trauma to these tissues and resulting pain and possibility of infection are relatively high. Still further, a standard thoracotomy may expose only one apex of the spinal curve to be corrected, thus requiring additional incisions or a longer initial incision in order to be able to fully treat the spine. Even where the apex of the spinal curve is adequately exposed and in good position relative to the thoracotomy for surgery, commonly adjacent vertebrae and intervertebral discs are not parallel to the exposure view provided by the thoracotomy, decreasing the effectiveness of the instrumentation used to correct the abnormal curvature. For these reasons, an endoscopic, thoracoscopic or other minimally invasive approach is preferable.
Accordingly, what is needed is a device and method that allows compression of orthopedic bone anchors through a single standard endoscopic, thoracoscopic or laparoscopic port.